This invention deals with a europium-activated phosphor including a rare earth oxyfluoride, which may be used in an X-ray image converter panel.
Conversion of an X-ray image into a visible image has, for a long time, been accomplished by directing the X-ray image onto a photographic film which has an emulsion of a silver salt as a photosensitive layer. The image can be improved by first converting the X-ray image into visible radiation using an X-ray image intensifying screen, and then projecting the visible radiation onto the photographic film. It would be desirable, however, to eliminate the use of photographic film altogether, because of the high cost of silver.
Phosphors are known which emit visible light when scanned or energized by visible or infrared radiation after having been exposed to ionizing radiation, such as X-rays. This phenomenon is called "stimulability," and the phosphors which possess this property are called stimulable phosphors.
A method of producing visible images using stimulable phosphors is disclosed in U.S. Pat. No. 3,859,527. X-rays passing through a subject illuminate a radiation image converting panel, storing a pattern of radiation in the phosphor particles of the panel. The stored pattern may be released as fluorescence when the phosphor particles are scanned or energized by visible or infrared radiation. The fluorescence, called stimulated radiation, is then sensed by a photomultiplier which converts it to electrical signals representative of the image. It is desirable, of course, that as small a dose of radiation as possible be given to the subject; and one way to reduce the amount of radiation is to use a phosphor which emits stimulated radiation of higher luminous intensity (I).
While X-ray intensifying screens are known which use a europium-activated alkaline earth metal fluoride halide phosphor (See Canadian Pat. No. 896,453 and U.S. Pat. No. 4,075,495), even this stimulable phosphor does not emit stimulated radiation of sufficient luminous intensity.